A method of encoding an audio signal includes HE-AAC (High Efficiency MPEG (Moving Picture Experts Group) 4 AAC (Advanced Audio Coding)) (ISO Standards/IEC 14496-3), AAC (MPEG2 AAC) (ISO Standards/IEC 13818-7), and the like.
For example, as the method of encoding the audio signal, a method has been proposed, in which low frequency encoding information obtained by encoding a low frequency component and high frequency encoding information for obtaining an estimated value of a high frequency component, which is generated from the low frequency component and the high frequency component, are output as a code obtained by encoding the audio signal (see, for example, Patent Document 1). In this method, the high frequency encoding information contains information required to calculate the estimated value of the high frequency component, such as a scale factor, an amplitude adjustment coefficient, and a spectral residual, for obtaining the high frequency component.
When decoding the code, the low frequency component obtained by decoding the low frequency encoding information and the high frequency component obtained by estimating the high frequency component based on information obtained by decoding the high frequency encoding information are combined to reproduce the audio signal.
In this type of encoding method, only the information for obtaining the estimated value of the high frequency component is encoded as information on a high frequency signal component, and hence the encoding efficiency can be improved while suppressing degradation of the sound quality.